Heretofore, compositions formed by mixing polyimide-based and polybenzoxazole-based resins having an excellent heat resistance, electrical insulation properties, and the like together with crosslinking compounds that are generally called thermal crosslinking agents have widely been used in a surface protective film and an interlayer dielectric film of semiconductor elements, an insulating layer of organic electroluminescence elements, and a flattening film of TFT substrates. These coating films are formed and then heat-baked, thereby crosslinking the resin to afford a thin film having an excellent heat resistance and mechanical characteristics.
In recent years, however, a significant problem has been posed, for example, in that, resulting from devices being made into thinner films, the composition shrinks during heat-baking, whereby the coated substrate undergoes an increased stress, generating a significant warpage and thus hindering automatic transport in the production processes. In response to this, it is anticipated that the shrinkage of the composition will be suppressed to make the warpage of the thin film smaller, by carrying out the heat-baking of the thin film at a low temperature of approximately 250° C. although it is usually carried out at a temperature of 350° C. or more.